One of the key elements of President Bush's address to the nation on Tuesday was his statement that the United States sees no distinction between those who commit acts of terrorism of the kind witnessed in the past few hours and those who harbour them.

It clearly suggests that if the Americans were to come to the conclusion, for example, that Osama bin Laden was behind the attacks then his host - the Taleban regime in Afghanistan - could not expect to be spared in any retaliatory measures the US might take.

But Mr Bush pointedly did not cast blame in any specific direction at this stage. He will have the lessons of recent history to ponder.

The attack is the sternest test of Mr Bush's presidency

The US blamed the 1998 bombings of its embassies in Nairobi and Dar-es-Salaam on followers of Mr Bin Laden, and it retaliated then with cruise missile attacks against targets in Afghanistan and Sudan.

The Afghanistan raid was on what was alleged to be a Bin Laden training camp but he escaped and it did not encourage the Taleban to hand him over.

The US found it hard to convince the world that it had hit a factory producing nerve gas in Sudan; Sudan itself said it was a pharmaceutical factory.

If he authorises any similar kind of retaliation now, once the source of these latest attacks becomes clearer, President Bush may be able to assuage some of the anger many Americans will be feeling in their aftermath.

But he also knows reprisals could backfire and could make the task of tackling the roots of terrorism more difficult.

Concerted action

If the declarations of condemnation of the New York and Washington attacks are all taken at face value this is one of the moments when there is something close to a global alliance for addressing the issue of terrorism and for concerted action to deal with it.

Bin Laden - accused of organising a series of attacks on the US

We have been here before after previous horrendous attacks with large numbers of civilian casualties and the rhetoric at the time has essentially remained rhetoric when it has come to formulating internationally agreed policy that might be effective.

It remains to be seen whether the almost apocalyptic nature of these latest attacks will do more to galvanise the international community.

President Bush was keen to talk up America's ability to get back on its feet again, even if it could do nothing to prevent an orchestrated attack of this kind.

Some in his country are talking of the new Pearl Harbour. They are comparing these events with a war.

Mr Bush has chosen a more measured line as he weighs his options. But he knows they may in reality be more limited than he would like.